Power-efficient media access techniques for wireless networks

ABSTRACT

Techniques for media access in wireless networks are disclosed. For instance, embodiments may provide a time interval for accessing a wireless communications channel. In addition, embodiments may prevent channel access during the time interval by stations incapable of employing a first channel access technique. This access technique employs an access probability P.

BACKGROUND

Wireless communications capabilities are increasingly being integratedinto portable devices, including laptop computers, handheld devices(such as personal digital assistants (PDAs)), and mobile phones. Theintegration of such capabilities can provide users with anywhere andanytime connectivity to information resources.

Power consumption is a key feature for such devices. For instance, lowerpower consumption levels correspond to increased operational timesbetween battery charging sessions. As a result of this, a device user'sexperience may be enhanced.

Wireless networks may employ media access techniques that are based oncarrier sensing. For example, networks provided by the Institute forElectrical and Electronics Engineers (IEEE) 802.11 standards may usecarrier sense multiple access with collision avoidance (CSMA/CA). InCSMA/CA, a device desiring to transmit first “listens” to a channel. Bylistening, the device determines whether the channel is “idle” or“busy”. If the device determines that the channel is idle, then it maysend its transmission. However, if the device determines that thechannel is busy, then it defers its transmission.

Unfortunately carrier sensing techniques, such as those used to performCSMA/CA, are not power-efficient.

BRIEF DESCRIPTION OF THE DRAWINGS

In the drawings, like reference numbers generally indicate identical,functionally similar, and/or structurally similar elements. The drawingin which an element first appears is indicated by the leftmost digit(s)in the reference number. The present invention will be described withreference to the accompanying drawings, wherein:

FIG. 1 is a diagram of an exemplary operational environment;

FIG. 2 is a diagram showing an exemplary timing format;

FIG. 3 is a flow diagram showing exemplary network operations;

FIG. 4 is a diagram showing the protection of managed contention accesszones;

FIG. 5 is a diagram of an exemplary station implementation; and

FIG. 6 is a diagram of an exemplary access point implementation.

DETAILED DESCRIPTION

Embodiments provide techniques for media access in wireless networks.For instance, embodiments may provide a time interval for accessing awireless communications channel. In addition, embodiments may preventchannel access during the time interval by stations incapable ofemploying a first channel access technique. This access techniqueemploys an access probability P. More particularly, the manner in whicha station transmits is based on this probability.

Through the employment of such techniques, reductions in powerconsumption may be advantageously achieved.

Reference throughout this specification to “one embodiment” or “anembodiment” means that a particular feature, structure, orcharacteristic described in connection with the embodiment is includedin at least one embodiment. Thus, appearances of the phrases “in oneembodiment” or “in an embodiment” in various places throughout thisspecification are not necessarily all referring to the same embodiment.Furthermore, the particular features, structures, or characteristics maybe combined in any suitable manner in one or more embodiments.

FIG. 1 is a diagram of an exemplary operational environment 100 in whichthe techniques disclosed herein may be employed. This environmentincludes various devices. More particularly, FIG. 1 shows an accesspoint (AP) 102, and multiple stations (STAs) 104 a-c. Together, thesedevices form a network 103. Operations of this network may be based onone or more IEEE 802.11 standards. However, embodiments are not limitedto this context.

Each of STAs 104 a-c communicates wirelessly with AP 102. In turn, AP102 operates as a bridge among STAs 104 a-c, as well as an interfacebetween STAs 104 a-c and devices outside of network 103. In the contextof IEEE 802.11, network 103 is referred to as a basic service set (BSS).

As described above, embodiments provide managed contention access (MCA)techniques, which may advantageously increase power efficiency. Each ofSTAs 104 a-c may be either a legacy station or an MCA-capable station.MCA-capable stations are able to recognize MCA-specific signaling andinformation. In contrast, legacy stations are not capable of recognizingany MCA-specific signaling and information.

FIG. 2 is a diagram showing an exemplary timing format 200 thatallocates the resources of a communications channel (e.g., a wirelessradio frequency channel). This format provides for the employment of MCAtechniques.

This format divides time into consecutive MCA periods. For instance,FIG. 2 shows a first MCA period 202 ₁ and a second MCA period 202 ₂. Inembodiments, first MCA period may begin at a predetermined time afterthe beginning of a beacon interval (e.g., an IEEE 802.11 beaconinterval).

Two zones exist within each of these MCA periods: an MCA zone, and alegacy zone. For instance, MCA period 202 ₁ includes an MCA zone 204 ₁,and a legacy zone 206 ₁. Similarly, MCA period 202 ₂ includes an MCAzone 204 ₂, and a legacy zone 206 ₂.

FIG. 2 shows that each MCA zone is further divided into multiple MCAintervals of equal duration. For instance, MCA zone 204 ₁ includes MCAintervals 208 a, 208 b, and 208 c. Likewise, MCA zone 204 ₂ includes MCAintervals 210 a, 210 b, and 210 c.

Each of these MCA intervals begins with an MCA slot. In particular, FIG.2 shows that MCA intervals 208 a, 208 b, and 208 c begin with MCA slots212 a, 212 b, and 212 c, respectively. Similarly, MCA intervals 210 a,210 b, and 210 c begin with MCA slots 214 a, 214 b, and 214 c,respectively.

By providing distinct legacy zones and MCA zones, the activities ofMCA-capable stations and legacy stations may be separated. Moreparticularly, during legacy zones, a legacy STA may access the channelthrough media access control techniques that are based on carriersensing. Such techniques may include, for example, media access controlin accordance with the IEEE 802.11 distributed coordination function(DCF) (which employs CSMA/CA). In embodiments, MCA-capable STAs may alsoaccess the channel during legacy zones by using such carrier sensingbased techniques.

However, during MCA zones, only MCA-capable STAs may access the channelthrough the employment of an MCA access technique. This technique mayinclude non carrier sensing approaches or/and carrier sensing basedapproaches.

In addition, FIG. 2 shows an access diagram 220 that is aligned withtiming format 200. This diagram shows when particular access techniquesare allowed. In particular, access diagram 220 shows that carriersensing (e.g., DCF access) is permitted during legacy zones. Incontrast, the MCA access technique is permitted the MCA zones. However,in embodiments, no access is allowed during MCA slots. Thus, the MCAslots operate as guard intervals to provide reliable operation in theevent of any synchronization errors. (excluding the MCA slots).

Various parameters are associated with the timing format of FIG. 2. Inembodiments, an access point may periodically provide stations with suchparameters. For example, an access point may deliver parameters inbeacons and/or access frames. Exemplary parameters are listed anddescribed in Table 1, below.

TABLE 1 Parameter Description T_(I) The employed MCA interval durationT_(S) The employed MCA slot duration T_(p) The employed MCA period timeduration P The MCA access probability N The number of MCA intervals perMCA period T_(start) The starting time of the first MCA interval,measured as the offset to the beginning of a beacon interval

The parameters of Table 1 may take on various values. In embodiments,such values may be based on an IEEE 802.11 time unit (TU), which is 1024microseconds (a beacon interval is usually 100 TUs). More particularly,the TU may be used as a granularity for adjusting such parameters (e.g.,T_(l), T_(p), N, T_(S), P, T_(start)). In embodiments, an access pointmay dynamically adjust parameters with such a granularity based onfactors, such as network conditions.

With respect to the setting of parameters, longer MCA slots may providegreater resistance to inaccurate clocking by stations. However,increases in MCA slot durations cause reductions in time available forcarrier sensing based access (e.g., DCF usage). On the other hand, theMCA usage is determined by the number and duration of MCA intervals.Hence, embodiments may set T_(S) as small as possible. For example, inIEEE 802.11 based networks, T_(S) may be set to the slot time (e.g. 9microseconds for 802.11a).

The parameters of Table 1 are provided for purposes of illustration, andnot limitation. Accordingly other additional or alternative parametersmay be employed. Moreover, the timing format of FIG. 2 is provided as anexample. Thus, other formats may be employed. Also, any number of legacyzones and MCA zones may be included in beacon intervals. Further, MCAzones may include any number of MCA intervals.

FIG. 3 illustrates an embodiment of a logic flow. In particular, FIG. 3illustrates a logic flow 300, which may be representative of theoperations executed by one or more embodiments described herein.Although FIG. 3 shows a particular sequence, other sequences may beemployed. Also, the depicted operations may be performed in variousparallel and/or sequential combinations.

The flow of FIG. 3 involves a media access in a network. Operations ofthis network may be based on one or more IEEE 802.11 standards. However,embodiments are not limited to this context. This network includes anaccess point, one or more legacy stations, and one or more MCA-capablestations. Accordingly, the flow of FIG. 3 may be employed in the networkof FIG. 1. Embodiments, however, are not limited to this context.

At a block 302, the access point provides a timing format for channelaccess by both MCA-capable stations and legacy stations. This timingformat includes one or more time intervals. Such time interval(s) mayinclude a first interval for a first access technique (e.g., an MCAtechnique), and a second interval for a second access technique (e.g.,CSMA/CA) With reference to FIG. 2, these first and second time intervalmay be an MCA zone, and a legacy zone respectively. However, embodimentsare not limited to the timing format of FIG. 2.

Thus, block 302 may comprise the access point sending initializationinformation to the stations (both legacy stations and MCA-capablestations) in the network. This initialization information may includeT_(l), T_(p), N, T_(S), P, and T_(start). However, other combinations ofinformation bay be sent. The access point may distribute thisinformation through beacon transmission(s) and/or through one or moremanagement frames.

At a block 304, the access point protects an MCA zone. In other words,the access point prevents the legacy stations from transmitting duringthe MCA zone. This may involve sending one or more transmissions thatinstruct the legacy stations to not transmit during the MCA zone. In thecontext of IEEE 802.11 networks, this may include a CTS-to-self message.This message reserves the medium until the end of the MCA zone. Inembodiments, the channel access for this CTS-to-self message shall startearly enough to accommodate the longest transmission opportunity (TXOP)employed in the network.

In addition, protecting the MCA zone may involve the access pointindicating to the MCA-capable stations that the MCA zone is availablefor transmission. For instance, as described above, the access point maytransmit a CTS-to-self message that reserves the MCA zone. To releasethis zone for the MCA-capable stations, the access point maysubsequently send a transmission that provides this feature. Forexample, embodiments provide a new control frame called MCA-Allowed. TheMCA-Allowed control frame may be sent with a short interframe spacing(SIFS) delay after the CTS-to-self message is sent.

As the MCA-Allowed control frame is new, it is not recognizable by thelegacy stations. Therefore, the legacy stations will continue to complywith the previously sent CTS-to self message. However, the MCA-capablestations will recognize this new control frame. Thus, the MCA-capablestations will be able to access the channel during the MCA zone.

At a block 306, the MCA-capable stations may access the channel duringthe MCA-zone. This channel access is in accordance with an MCA accesstechnique. Moreover, in accordance with this technique, any transmissionof MCA-capable stations has to complete before the beginning of the MCAslot in the nearest future.

This technique provides three channel access options. More particularly,an MCA zone provides the following three channel access optionsdepending on the value of P, (i.e. whether 0<P<1, P=0, or P=1). Asdescribed above, P is provided by the access point at block 302.

According to the first option (0<P<1), an MCA-capable station attemptsto access the channel (i.e., transmit) during the MCA zone according toa probability-based technique. In particular, the MCA-capable stationrandomly generates a number, X. In embodiments, this number may begenerated in accordance with a random variable that is uniformlydistributed between 0 and 1.

If X is less than P (the MCA access probability), then the MCA-capablestation may start transmitting within the MCA zone (right after the MCAslot) without conducting any carrier sensing. Otherwise, if X is greaterthan or equal to P, the MCA-capable station must use the carrier sensingbased approach (e.g., DCF) to access the channel. Once any resultingcontention-based transmissions are complete and there is sufficient timeremaining in the MCA interval, an MCA-capable station may employ thecarrier sensing based approach (e.g., DCF) to access the channel.

As described above, P may be provided to the MCA capable station atblock 302. In embodiments, P may be set to zero (the second option).This effectively disables contention for channel access right after theend of each MCA slot. Thus, when this setting is employed, the accesspoint may send out a poll frame right after the MCA slot to request oneor more individual stations to transmit. Once any resulting pollingtransmissions are complete and there is sufficient time remaining in theMCA interval, an MCA-capable station may employ the carrier sensingbased approach (e.g., DCF) to access the channel.

According to the third option (P=1), an MCA-capable STA may employ DCFimmediately after each MCA slot, and the last channel busy time shouldbe set to the end of the MCA slot. As described above, DCF involveschannel access through CSMA/CA.

At a block 308, the both the MCA-capable stations and the legacystations may access the channel during a legacy zone. More particularly,both of these station types employ DCF during the legacy zone.

Thus, the flow of FIG. 3 demonstrates channel access techniques that areavailable to stations during various portions of MCA zones and legacyzones. Table 2, below, provides a summary of these techniques.

TABLE 2 MCA Zone Legacy Zone Legacy Station No channel access Carriersensing based access MCA-capable MCA access Carrier sensing basedStation access

As indicated above, MCA-capable stations do not necessarily sample thecommunications medium (e.g., perform carrier sensing) during MCAinterval. Instead, through the employment of probability-based accesstechniques, such stations may simply “wake up” and transmit (when X isless than P). Thus, MCA zone transmissions from two or more stations maycollide.

In embodiments, the access point may determine parameters to yield achosen probability of collision. Such parameters may include (but arenot limited to) the number of MCA slots within an MCA zone and theprobability P. The access point may determine such parameters based onvarious factors. Exemplary factors include network conditions, such asthe number of MCA-capable stations in the access point's network,traffic patterns associated with such MCA-capable stations, and soforth. The traffic patterns of the MCA-capable stations may beestablished with a modified IEEE 802.11e TSPEC exchange. From suchtraffic patterns, collision statistics for various parameters may beascertained. More particularly, such collision statistics should reflectcollision statistics of the slotted-aloha protocol.

FIG. 4 is a diagram showing MCA zones of FIG. 2 being protected. Inparticular, this diagram shows messages sent from an access point (notshown). Further, this diagram shows the effect of these messages on alegacy station 402, and on an MCA-capable station 404.

As shown in FIG. 4, prior to MCA zone 204 ₁, the access point sends aCTS-to-self message 406 a, and an MCA allowed message 408 a. As shown inFIG. 4, legacy station 402 then considers the channel busy from thispoint until the beginning of legacy zone 206 ₂. However, from theperspective of MCA-capable station 404, the channel is merely busyduring the reception of these messages. Similarly, prior to MCA zone 204₂, the access point sends a CTS-to-self message 406 b, and an MCAallowed message 408 b. In turn, legacy station considers the channelbusy throughout MCA zone 204 ₂, while MCA-capable station 404 merelyconsiders the channel busy during the reception of these messages.

FIG. 5 is a diagram of an implementation 500 that may be included in anMCA-capable station. However, this implementation may be also employedin other contexts. Implementation 500 may include various elements. Forexample, FIG. 5 shows implementation 500 including an antenna 502, atransceiver module 504, a host module 506, and an access selectionmodule 508. These elements may be implemented in hardware, software, orany combination thereof.

Antenna 502 provides for the exchange of wireless signals with remotedevices. Although a single antenna is depicted, multiple antennas may beemployed. For example, embodiments may employ one or more transmitantennas and one or more receive antennas. Alternatively oradditionally, embodiments may employ multiple antennas for beamforming,and/or phased-array antenna arrangements.

As shown in FIG. 5, transceiver module 504 includes a control module509, a transmitter portion 510, and a receiver portion 512. Duringoperation, transceiver module 504 provides an interface between antenna502 and host module 506. For instance, transmitter portion 510 receivessymbols 520 from host module 506, and generates corresponding signals522 for wireless transmission by antenna module 502. This may involveoperations, such as modulation, amplification, and/or filtering.However, other operations may be employed.

Conversely, receiver portion 512 obtains signals 524 received by antenna502 and generates corresponding symbols 526. In turn, transceiver module504 provides symbols 526 to host module 506. This generation of symbols526 may involve operations, including (but not limited to) demodulation,amplification, and/or filtering.

Signals 522 and 524 may be in various formats. For instance, thesesignals may be formatted for transmission in IEEE 802.11 networks.However, embodiments are not limited to these exemplary networks.

To provide such features, transmitter portion 510 and receiver portion512 may each include various components, such as modulators,demodulators, amplifiers, filters, buffers, upconverters, and/ordownconveters. Such components may be implemented in hardware (e.g.,electronics), software, or any combination thereof.

The symbols exchanged between host module 506 and transceiver module 504may form messages or information associated with one or more protocols,and/or with one or more user applications. Thus, host module 506 mayperform operations corresponding to such protocol(s) and/or userapplication(s). Exemplary protocols include various media accesscontrol, network, transport and/or session layer protocols. Exemplaryuser applications include telephony, messaging, e-mail, web browsing,content (e.g., video and audio) distribution/reception, and so forth.

Moreover, in transmitting signals 522, transceiver module 504 may employvarious access techniques. For example, transceiver module 504 mayemploy a first channel access technique (e.g., an MCA technique).Alternatively, transceiver module 504 may employ a second channel accesstechnique that includes carrier sensing. In embodiments, the firstchannel access technique may be the probability-based access techniquedescribed herein, and the second channel access technique may be CSMA/CA(e.g., DCF). Embodiments, however, are not limited to these techniques.In embodiments, selection among such techniques is performed by accessselection module 508. Details regarding such selections are providedbelow.

In addition to operating as an interface between host module 506 andantenna 502, transceiver module 504 may perform various signaling, linkcontrol, and media access operations. For instance, transceiver module504 may exchange (via antenna 502) information with remote devices. Suchinformation may include beacons, control frames, signaling messages, andso forth.

As described above, transceiver module 504 includes a control module509. This module manages various operations of transceiver module 504.For example, control module 509 manages the employment of various mediaaccess techniques. FIG. 5 shows that control module 509 is coupled totransmitter portion 510 and receiver portion 512. Accordingly, controlmodule 509 may coordinate or perform operations, such as carrier sensingand the reception of media access parameters. In embodiments, suchoperations may involve both transmitter portion 510 and receiver portion512.

FIG. 5 shows that control module 509 sends initialization information530 to access selection module 508. This initialization information isoriginated by a remote access point and received by receiver portion 512(via antenna 502). As described above (e.g., with reference to block 302of FIG. 3), this initialization information may include parameters, suchas timing information, access probability P, as well as otherinformation.

Upon receipt of initialization information 530, access selection module508 may establish synchronization with its corresponding timing format.Through this synchronization, access selection module 508 determineswhen transceiver module 504 may employ particular access techniques. Asshown in FIG. 5, access determination module 508 sends an accessselection directive 532 to control module 509.

This directive indicates which access technique may be employed bytransceiver module 504. For example, in the context of FIG. 2, directive532 may indicate a non-carrier sensing based access technique during MCAintervals.

FIG. 6 is a diagram of an implementation 600 that may be included in anaccess point. However, this implementation may be also employed in othercontexts. Implementation 600 may include various elements. For example,FIG. 6 shows implementation 600 including an antenna 602, a transceivermodule 604, a host module 606, and an access management module 608.These elements may be implemented in hardware, software, or anycombination thereof.

Antenna 602 provides for the exchange of wireless signals with remotedevices. Although a single antenna is depicted, multiple antennas may beemployed. For example, embodiments may employ one or more transmitantennas and one or more receive antennas. Alternatively oradditionally, embodiments may employ multiple antennas for beamforming,and/or phased-array antenna arrangements.

As shown in FIG. 6, transceiver module 604 includes a control module609, a transmitter portion 610, and a receiver portion 612. Transmitterportion 610 and receiver portion 612 may operate in manner similar totransmitter portion 510 and receiver portion 512 of FIG. 5.

For instance, FIG. 6 shows transmitter portion 610 receiving symbols 620from host module 606 and generating corresponding signals 622 forwireless transmission by antenna module 602. Conversely, receiverportion 612 obtains signals 624 received by antenna 602 and generatescorresponding symbols 626, which are provided to host module 606. Inperforming these operations, features described above with reference toFIG. 5 may be employed.

In addition, transmitter portion 610 may generate signals 622 based onmessages provided by control module 609. Such messages may correspond totransmissions that establish media access characteristics. Detailsregarding this feature are provided below.

Signals 622 and 624 may be in various formats. For instance, thesesignals may be formatted for transmission in IEEE 802.11 networks.However, embodiments are not limited to these exemplary networks.

The symbols exchanged between host module 606 and transceiver module 604may form messages or information associated with one or more protocols,and/or with one or more user applications. Thus, host module 606 mayperform operations corresponding to such protocol(s) and/or userapplication(s). Exemplary protocols and user applications are describedabove with reference to FIG. 5. In addition, host module 606 may providean interface to outside networks for the wireless stations.

Access management module 608 determines various media accesscharacteristics to be employed in a wireless network. For instance,access management module 608 determines a timing format, such as thetiming format of FIG. 2. As described herein, this timing format mayinclude one or more time intervals, each interval having one or morefirst portions for a first channel access technique (e.g., a non-carriersensing based technique), and one or more second portions for a secondchannel access technique (e.g., a carrier sensing based technique). Withreference to FIG. 2, these time interval(s) may be an MCA zone(s).However, embodiments are not limited to the timing format of FIG. 2.

Also, access management module 608 may determine one or more furtheraccess parameters. For example, access management module 608 maydetermine the access probability P. In embodiments, however, accessmanagement module 608 may determine additional or alternativeparameters.

The timing format and/or access parameter(s) may be determined based onone or more network conditions. As described herein, such conditions mayinclude traffic patterns of stations (e.g., MCA-capable stations and/orlegacy stations). Access management module 608 may obtain data regardingsuch patterns through the monitoring of wireless transmissions exchangedby transceiver module 604. In FIG. 6, this feature is shown as networkconditions 630 being indicated to access management module 608.

Based on the above determinations, access management module 608 sendstransceiver module 604 an access management directive 632. In turn,transceiver module 604 generates corresponding transmissions, which aresent (e.g., broadcast) to receiving stations. For instance, controlmodule 609 of transceiver module 604 generates messages (e.g., beacons,access frames, and so forth) that include information, (such as theparameters of Table 1) for stations (e.g., MCA-capable stations) tooperate in accordance with the access characteristics determined byaccess management module 608. In turn, transmitter portion 610 generatescorresponding signals 624 that are wirelessly transmitted via antenna602.

The implementations of FIGS. 5 and 6 are provided for purposes ofillustration, and not limitation. Thus other implementations may beemployed. For instance, implementations may include combinations offeatures of FIGS. 5 and 6.

As described herein, various embodiments may be implemented usinghardware elements, software elements, or any combination thereof.Examples of hardware elements may include processors, microprocessors,circuits, circuit elements (e.g., transistors, resistors, capacitors,inductors, and so forth), integrated circuits, application specificintegrated circuits (ASIC), programmable logic devices (PLD), digitalsignal processors (DSP), field programmable gate array (FPGA), logicgates, registers, semiconductor device, chips, microchips, chip sets,and so forth.

Examples of software may include software components, programs,applications, computer programs, application programs, system programs,machine programs, operating system software, middleware, firmware,software modules, routines, subroutines, functions, methods, procedures,software interfaces, application program interfaces (API), instructionsets, computing code, computer code, code segments, computer codesegments, words, values, symbols, or any combination thereof.

Some embodiments may be implemented, for example, using amachine-readable medium or article which may store an instruction or aset of instructions that, if executed by a machine, may cause themachine to perform a method and/or operations in accordance with theembodiments. Such a machine may include, for example, any suitableprocessing platform, computing platform, computing device, processingdevice, computing system, processing system, computer, processor, or thelike, and may be implemented using any suitable combination of hardwareand/or software.

The machine-readable medium or article may include, for example, anysuitable type of memory unit, memory device, memory article, memorymedium, storage device, storage article, storage medium and/or storageunit, for example, memory, removable or non-removable media, erasable ornon-erasable media, writeable or re-writeable media, digital or analogmedia, hard disk, floppy disk, Compact Disk Read Only Memory (CD-ROM),Compact Disk Recordable (CD-R), Compact Disk Rewriteable (CD-RW),optical disk, magnetic media, magneto-optical media, removable memorycards or disks, various types of Digital Versatile Disk (DVD), a tape, acassette, or the like. The instructions may include any suitable type ofcode, such as source code, compiled code, interpreted code, executablecode, static code, dynamic code, encrypted code, and the like,implemented using any suitable high-level, low-level, object-oriented,visual, compiled and/or interpreted programming language.

While various embodiments of the present invention have been describedabove, it should be understood that they have been presented by way ofexample only, and not in limitation. For example, the techniquesdescribed herein are not limited to IEEE 802.11 networks.

Accordingly, it will be apparent to persons skilled in the relevant artthat various changes in form and detail can be made therein withoutdeparting from the spirit and scope of the invention. Thus, the breadthand scope of the present invention should not be limited by any of theabove-described exemplary embodiments, but should be defined only inaccordance with the following claims and their equivalents.

The invention claimed is:
 1. A method, comprising: providing a timeinterval for accessing a wireless communications channel; preventingchannel access during the time interval by stations incapable ofemploying a first channel access technique, wherein the first channelaccess technique comprises a non-carrier sensing technique, wherein saidpreventing channel access comprises: sending a first transmission toreserve the channel during the time interval; and sending a secondtransmission to release the channel during the time interval, the secondtransmission comprising a control frame that is not recognizable bystations incapable of employing the first channel access technique; andsending a first message to instruct a first station capable of employingthe first channel access technique to employ the first channel accesstechnique during a first subinterval of the time interval, wherein anytransmission of the first station has to complete before start of asecond subinterval of the time interval.
 2. The method of claim 1,further comprising: providing a further time interval for a carriersensing technique.
 3. The method of claim 1, comprising sending a secondmessage to instruct a second station capable of employing the firstchannel access technique to employ a carrier sensing technique during asecond subinterval of the time interval, based on a comparison of arandomly generated value for the second station with an accessprobability P, wherein the carrier sensing technique comprises carriersense multiple access with collision avoidance (CSMA/CA).
 4. The methodof claim 3, further comprising transmitting initialization information,the initialization information, comprising P.
 5. The method of claim 4,further comprising determining P based on one or more networkconditions.
 6. The method of claim 1, further comprising determining oneor more characteristics of the time interval.
 7. The method of claim 6,wherein the one or more characteristics of the time interval aredetermined based on one or more network conditions.
 8. An apparatus,comprising: an access management module to determine a time interval foraccessing a wireless communications channel, the access managementmodule operative on a transceiver to: send one or more transmissions toprotect the time interval from access by stations incapable of employinga first channel access technique, wherein the first channel accesstechnique comprises a non-carrier sensing technique, wherein the one ormore transmissions include: a first transmission to reserve the channelduring the time interval; and a second transmission to release thechannel during the time interval, the second transmission comprising acontrol frame that is not recognizable by stations incapable ofemploying the first channel access technique; and send a first messageto instruct a first station capable of employing the first channelaccess technique to employ the first channel access technique during afirst subinterval of the time interval, wherein any transmission of thefirst station has to complete before start of a second subinterval ofthe time interval.
 9. The apparatus of claim 8, the access managementmodule operative on a transceiver to send a second message to instruct asecond station capable of employing the first channel access techniqueto employ a second channel access technique during a second subintervalof the time interval, based on a comparison of a randomly generatedvalue for the second station with an access probability P, wherein theaccess management module is to determine one or more characteristics ofthe time interval and P, the determination based on one or more networkconditions.
 10. An article comprising a machine-accessiblenon-transitory medium having stored thereon instructions that, whenexecuted by a machine, cause the machine to: provide a time interval foraccessing a wireless communications channel; prevent channel accessduring the time interval by stations incapable of employing a firstchannel access technique, wherein the first channel access techniquecomprises a non-carrier sensing technique, wherein said preventingchannel access comprises: sending a first transmission to reserve thechannel during the time interval; and sending a second transmission torelease the channel during the time interval, the second transmissioncomprising a control frame that is not recognizable by stationsincapable of employing the first channel access technique; and send afirst message to instruct a first station capable of employing the firstchannel access technique to employ the first channel access techniqueduring a first subinterval of the time interval, wherein anytransmission of the first station has to complete before start of asecond subinterval of the time interval.
 11. The article of claim 10,comprising instructions that, when executed by a machine, cause themachine to send a second message to instruct a second station capable ofemploying the first channel access technique to not employ the firstchannel access technique and to employ a second channel access techniqueduring a second subinterval of the time interval, wherein the secondchannel access technique comprises carrier sense multiple access withcollision avoidance (CSMA/CA).